Use a mild detergent solution applied with a window brush or a white scrubbing pad. If you have access to a pressure washer or vapor cleaner, that too, will lessen your time. Just be sure to turn down the pressure (300 PSI) and keep the nozzle back from the glass at least 12 inches or you could damage the seal around the glass and get water inside the space. If this doesn''t work specialty aluminum cleaning products and course pads are available, however, they are ... — Lynn E. Krafft, ICAN/ATEX Editor